Abstract
The exponential Phan–Tien and Tanner (PTT), Giesekus, Leonov, and modified extended Pom–Pom (mXPP) differential constitutive models are evaluated in two ways: with regard to steady shear characteristics and with regard to large amplitude oscillatory shear characteristics of a solution of poly(ethylene oxide) in dimethyl sulfoxide. Efficiency of the models with nonlinear parameters optimized with respect to steady shear measurements is evaluated by their ability to describe large amplitude oscillatory shear (LAOS) characteristics. The reciprocal problem is also analyzed: The nonlinear parameters are optimized with respect to the LAOS measurements, and the models are confronted with the steady shear characteristics. In this case, optimization is based on the LAOS measurements and equal emphasis is placed on both real and imaginary parts of the stress amplitude. The results show that the chosen models are not adequately able to fit the LAOS characteristics if the optimization of nonlinear parameters is based on steady shear measurements. It follows that the optimization of nonlinear parameters is much more responsible if it is carried out with respect to the LAOS data. In this case, when the optimized parameters are used for a description of steady shear characteristics, efficiency of the individual models as documented differs.
Highlights
Differential constitutive models are quite often confronted only with the rheological characteristics of polymeric materials exposed to relatively moderate deformation
The results show that the chosen models are not adequately able to fit the large amplitude oscillatory shear (LAOS) characteristics if the optimization of nonlinear parameters is based on steady shear measurements
A shift from analysis of flow behavior in the purely linear viscoelastic region to the non-linear region was enabled by the onset of more ingenious measurements represented by large amplitude oscillatory shear (LAOS) data
Summary
Differential constitutive models are quite often confronted only with the rheological characteristics of polymeric materials exposed to relatively moderate deformation. In polymer processing, we encounter deformation in higher orders In this respect, a shift from analysis of flow behavior in the purely linear viscoelastic region to the non-linear region was enabled by the onset of more ingenious measurements represented by large amplitude oscillatory shear (LAOS) data (initiated already a few decades ago [1,2,3,4,5,6]). A shift from analysis of flow behavior in the purely linear viscoelastic region to the non-linear region was enabled by the onset of more ingenious measurements represented by large amplitude oscillatory shear (LAOS) data (initiated already a few decades ago [1,2,3,4,5,6]) This provides a possibility of more thorough evaluation of the individual constitutive models due to the remarkable extension of applied deformation. The optimized values of nonlinear parameters of the studied constitutive models are used for a comparison with the steady shear characteristics and vice versa, the parameters optimized for a description of steady shear characteristics are applied for a comparison with the LAOS measurements
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